The present invention pertains to an oxygen fueled combustion system. More particularly, the present invention pertains to an oxy-fueled combustion system in which the production of green-house gases is reduced and in which fossil fuel consumption is reduced.
Oxygen fueled burner systems are known, however, their use is quite limited. Oxy-fueled burner systems are generally only used in those applications in which extremely high flame temperatures are required. For example, these systems may be used in the glass making industry in order to achieve the temperatures necessary to melt silica to a fusion temperature. Otherwise, it is commonly accepted that structural and material limitations dictate the upper temperatures to which many industrial systems can be subjected. To this end, air fueled or air fired combustion systems are used in boilers, furnaces and the like throughout most every industrial application including manufacturing, electric power generating and other process applications.
In particular, air fueled combustion systems or electric heating systems are used throughout the steel and aluminum making industries, as well as the power generation industry, and other industries that rely upon carbon based fuels. In air fueled systems, air which is comprised of about 79% nitrogen and 21% oxygen, is fed, along with fuel into a furnace. The air fuel mixture is ignited creating a continuous flame. The flame transfers energy in the form of heat from the fuel air mixture into the furnace.
In the steel and aluminum industries, air fueled furnaces and electric furnaces have been used as the primary heat source for creating molten metals. With respect to air fueled furnaces, it is conventionally accepted that the energy requirements, balanced against the thermal limitations of the process equipment, mandate or strongly support the use of these types of combustion systems. As to the use of electric furnaces in the aluminum industry, again, conventional wisdom supports this type of energy source to achieve the temperatures necessary for aluminum processing.
One drawback to the use of air fueled combustion systems, is that these systems produce NOx and other green-house gases such as carbon dioxide, sulfur dioxide and the like, as an inherent result of the combustion process. NOx and other green-house gases are a large contributor to environmental pollution, including, but not limited to acid rain. As such, the reduction in emission of NOx and other green-house gases is desirable, and as a result of regulatory restrictions, emission is greatly limited. To this end, various devices must be installed on these combustion systems in order to limit and/or reduce the levels of NOx and other green-house gases produced.
Another drawback with respect to air fueled furnaces is that much of the energy released from the combustion process is absorbed or used to heat the gaseous nitrogen present in the air that is fed to the furnace. This energy is essentially wasted in that the heated nitrogen gas is typically, merely exhausted from the heat source, e.g., furnace. To this end, much of the energy costs are directed into the environment, through an off-gas stack or the like. Other drawbacks of the air fed combustion systems known will be recognized by skilled artisans.
Electric furnaces likewise have their drawbacks. For example, inherent in these systems as well is the need for a source of electricity that is available on a continuous basis, essentially without interruption. In that large amounts of electric power are required to operate electric furnaces, it is typically necessary to have these electric furnaces located in proximity to electric generating plants and/or large electrical transmission services. In addition, electric furnaces require a considerable amount of maintenance to assure that the furnaces are operated at or near optimum efficiency. Moreover, inherent in the use of electric furnaces is the inefficiency of converting a fuel into electrical power (most large fossil fueled power stations that use steam turbines operate at efficiencies of less than about 40 percent, and generally less than about 30 percent). In addition, these large fossil fueled stations produce extremely large quantities of NOx and other green-house gases.
For example, in the aluminum processing industry, and more specifically in the aluminum scrap recovery industry, conventional wisdom is that flame temperatures in furnaces should be maintained between about 2500° F. and 3000° F. This range is thought to achieve a balance between the energy necessary for providing sufficient heat for melting the scrap aluminum, and maintaining adequate metal temperatures in the molten bath at about 1450° F. Known furnaces utilize a design in which flame temperatures typically do not exceed 3000° F. to assure maintaining the structural integrity of these furnaces. That is, it is thought that exceeding these temperature limits can weaken the support structure of the furnace thus, possibly resulting in catastrophic accidents. In addition, stack temperatures for conventional furnaces are generally about 1600° F. Thus, the temperature differential between the flame and the exhaust is only about 1400° F. This results in inefficient energy usage for the combustion process.
It is also believed that heat losses and potential damage to equipment from furnaces in which flame temperatures exceed about 3000° F. far outweigh any operating efficiency that may be achieved by higher flame temperatures. Thus, again conventional wisdom fully supports the use of air fueled furnaces in which flame temperatures are at an upper limit of about 3000° F. (by flame stoichiometry) which assures furnace integrity and reduces energy losses.
Accordingly, there exists a need for a combustion system that provides the advantages of reducing environmental pollution (attributable to NOx and other green-house gases) while at the same time providing efficient energy use. Desirably, such a combustion system can be used in a wide variety of industrial applications, ranging from the power generating utility industry to chemical processing industries, metal production and processing and the like. Such a combustion system can be used in metal, e.g., aluminum, processing applications in which the combustion system provides increased energy efficiency and pollution reduction. There also exists a need, specifically in the scrap aluminum processing industry for process equipment (specifically furnaces) that are designed and configured to withstand elevated flame temperatures associated with such an efficient combustion system and to increase energy efficiency and reduce pollution production.